I noticed a problem with my CX211 when using it with a 5d mark II. If I tap the microphone to where it overloads the preamp, any audio recorded after has electrical static. I do not remember having this problem when I first got the unit. Is it going bad? Anyone have something like this happen to their unit?

The problem could be in the CX211 or in the camera. To test it, I recommend connecting the CX211 to a laptop or PC mic input. Adjust the PC input gain so it is recording at levels similar to the 5D. Record the input, tap the microphone and check the recording. If it's clean, the problem is probably in the camera. If not, the CX211 is the likely location.

Also use a fresh battery, make sure the battery connection is clean, and check your cable and connections.